1. Field of the Invention
The present invention relates to a method of producing a multilayer interconnection board, and particularly, to a method of producing a multilayer interconnection board including the steps of processing a resin member on an interconnection by imprinting press, and removing residue of the resin member at the bottom of a via hole after forming the via hole.
2. Description of the Related Art
Along with requirements of enhanced performance and decreased size of recent electronic communication apparatuses, development has been made in the field of printed circuit boards, specifically, a multilayer interconnection board on which plural layers of interconnection circuits are stacked to increase density of the circuits. For example, there is a kind of multilayer interconnection board produced by a so-called “built-up method”, in which interconnection layers and insulating layers are stacked alternately, and vias are provided between an upper interconnection layer and a lower interconnection layer for connecting the two interconnection layers.
A via is formed by filling a hole (a via hole) opened in an insulating layer with metal for the purpose of connection between conductive materials separated by the insulating layer. Usually, the via hole can be formed by a laser (the so-called laser processing), or can be formed by using a tool (the so-called imprinting press). With the imprinting press using a tool, because via holes and interconnection grooves can be formed in the same layer at the same time, and fabrication cost is low because it is not necessary to use expensive laser processing apparatuses, so that this method has attracted attention recently.
Below, descriptions are made of a process of forming a multilayer interconnection board by imprinting press using a tool in the related art with reference to FIG. 1 through FIG. 5.
FIG. 1 is a schematic cross-sectional view showing a step of a process of forming a multilayer interconnection board in the related art.
As illustrated in FIG. 1, an interconnection 12 and resin 13 are formed on a substrate 11 sequentially.
FIG. 2 is a schematic cross-sectional view showing a step of the process of forming the multilayer interconnection board in the related art.
As illustrated in FIG. 2, a tool 15 having a projecting portion 16 for forming a via hole is pressed against the resin 13 to perform imprinting press.
FIG. 3 is a schematic cross-sectional view showing a step of the process of forming the multilayer interconnection board in the related art.
As illustrated in FIG. 3, the tool 15 is removed after the resin 13 cures, and thereby, the via hole 18 is formed.
Because the resin 13 exists between the projecting portion 16 and the interconnection 12, a resin layer 17 remains at the bottom of the via hole 18. Further, in FIG. 3, a reference number 19A indicates a side wall of the via hole 18.
With the residual resin layer 17 being present, even when the via hole is filled with metal and a via is formed, because the resin layer 17 is insulating, the via and the interconnection 12 are not electrically connected.
FIG. 4 is a schematic cross-sectional view showing a step of removing the residual resin layer 17 in the process of forming the multilayer interconnection board in the related art.
Because the via and the interconnection 12 cannot be electrically connected due to existence of the residual resin layer 17, as a solution to this problem, in the related art, as illustrated in FIG. 4, a step is carried out of removing the residue of the resin layer 17 on the interconnection 12 after imprinting press with the tool 15.
In FIG. 4, a letter “A” indicates the position of the via hole 18 after imprinting press with the tool 15, a reference number 19B indicates a side wall of the via hole (represented by a reference number 20) after the resin layer 17 is removed. When removing the resin layer 17, a resin solvent is used, and by this removing step, the interconnection 12 is exposed through the via hole 20.
FIG. 5 is a schematic cross-sectional view showing a step in the process of forming the multilayer interconnection board in the related art.
Following the step in FIG. 4, the via hole 20 is filled with metal and a via 21 is formed on the interconnection 12, thus, the via 21 and the interconnection 12 are electrically connected.
If forming the via hole by a laser, there is still resin remaining on the interconnection, although it is not so much compared with the above imprinting press using a tool. Therefore, similarly, the step of removing the residual resin is performed by using the resin solvent. This is described in Japanese Laid Open Patent Application No. 10-117058.
However, when removing the resin layer 17 by using the resin solvent, as illustrated in FIG. 4, the resin 13, which constitutes the via hole 18, is also dissolved, hence, the side wall 19A of the via hole 18 broadens in the crosswise direction, and the side wall moves to the position 19B. That is, the via hole 20 ends up being larger than a desired size. Even when forming the via hole by a laser, because the same step is carried out of removing the residual resin by using the resin solvent, the same problem arises in that the obtained via hole ends up being larger than a desired size.